Extension of the interval between vaccine doses for the BNT162b2 mRNA vaccine was introduced in the UK to accelerate population coverage with a single dose. At this time, trial data was lacking, and we addressed this in a study of UK healthcare workers. The first vaccine dose induced protection from infection from the circulating alpha (B.1.1.7) variant over several weeks. In a sub-study of 589 individuals, we show that this single dose induces SARS-CoV-2 neutralizing antibody (NAb) responses and a sustained B and T cell response to spike protein. NAb levels were higher after the extended dosing interval (6-14 weeks) compared to the conventional 3-4 week regimen, accompanied by enrichment of CD4+ T cells expressing IL2. Prior SARS-CoV-2 infection amplified and accelerated the response. These data on dynamic cellular and humoral responses indicate that extension of the dosing interval is an effective, immunogenic protocol. After giving a primary dose, delaying administration of a second dose of BNT162b2 COVID-19 vaccine up to 6-14 weeks continues to provide strong protection and contributes to favorable antibody, B cell, and T cell responses.
